The present invention relates to a method and apparatus for making dripper lines as widely used in drip irrigation systems. The method and apparatus of the present invention are particularly useful for making dripper lines having the flat-type dripper units (i.e., non-cylindrical dripper units), and are therefore described below with respect to this application.
Dripper lines including the flat-type dripper units (i.e., non-cylindrical dripper units) have been in use for approximately 20 years and are extensively described in the patent literature, as shown, for example, by U.S. Pat. Nos. 4,728,042 and 4,307,841. A number of processes and apparatus have been developed for making such dripper lines, as described, for example, in U.S. Pat. Nos. 5,022,940, 5,122,044, 5,271,786, 5,282,916, 5,324,371 and 5,324,379.
An object of the present invention is to provide another method and apparatus for making such dripper lines, which method and apparatus have a number of advantages, as will be described more particularly below.
According to one aspect of the present invention, there is provided a method of making a dripper line, comprising: extruding a tube through a calibrator; feeding a plurality of dripper units into the extruded tube and into contact with its inner surface; heat welding the dripper units to longitudinally spaced locations on the inner surface of the tube; and forming outlet openings in the tube communicating with the dripper units; characterized in that the dripper units are fed into the extruded tube so as to have a linear velocity, at the instant of their initial contact with the inner surface of the tube, which is greater than the linear velocity of the inner surface of the tube where initially contacted by the dripper units.
As will be described more particularly below, such a method provides a number of advantages. Thus, the above-cited U.S. Pat. Nos. 5,022,940, 5,122,044 and 5,324,371 describe feeding the dripper units so that their linear velocity, at the instant of initial contact with the inner surface of the extruded tube, is substantially equal to the linear velocity of the inner surface of the tube contacted by the dripper units in order to aviod weakening the extruded tube, which could obviously occur if the dripper units are travelling at a smaller linear velocity than the extruded tube. However, by making the linear velocity of the dripper units higher than that of the extruded tube at the instant of initial contact, this excess velocity of the dripper units aids the extruded tube in overcomming the resistance to which the extruded tube is subjected during its extrusion, and thereby avoids weakening the tube that may be caused by this resistance. In addition, the foregoing feature of the present invention enables the dripper units to be fed at a faster rate, and thereby enables higher productivity in the extrusion line.
Preferably, the linear velocity of the dripper units at the instant of their initial contact with the extruded tube should be from 15% to 75% greater than the linear velocity of the contacted surface of the extruded tube. The excess velocity would depend on a number of factors, particularly the resistance of the tube at that location of the extrusion process. It is anticipated that in some applications, the excess velocity would be in the order of 30%, and in other applications it would be in the order of 60%.
According to further features in the preferred embodiments of the invention described below, the extruded tube is extruded at a first diameter and is reduced in diameter as it passes through the calibrator. The entrance opening of the calibrator has a tapered surface decreasing in diameter in the downstream direction with respect to the entrance opening to allow limited outward deformation of the extruded tube when initially contacted by the dripper unit.
According to further features in some described preferred embodiments, the calibrator unit includes a backing surface engaging the outer surface of the extruded tube downstream of the entrance opening of the calibrator unit to limit outward deformation of the extruded tube when initially contacted by a dripper unit. Preferably, the backing surface is a moving backing surface, moving at the same linear velocity as the extruded tube where contacted by the dripper unit, and is located within the calibrator, preferably 20-50 mm downstream of the initial contact of the extruded tube with the calibrator.
According to another aspect of the invention, there is provided a method of making a dripper line, comprising: extruding a tube; feeding a plurality of dripper units into the tube and into contact with its inner surface at the time of extruding the tube; heat welding the dripper units to longitudinally spaced locations on the inner surface of the tube; and forming outlet openings in the tube communicating with the dripper units; characterzied in that each dripper unit is heat welded to the extruded tube by feeding the dripper units between a track within the extruded tube and a moving backing surface externally of the extruded tube; the distance between the moving backing surface and the track determining the final thickness of the extruded tube and dripper unit welded thereto.
The invention also provides apparatus for making dripper lines in accordance with the above method.
Further features and advantages of the invention will be apparent from the description below.